With ex-Arsenal footballer Sol Campbell coming out in favour of a Brexit, the Leave camp must now tackle mixed messages

Sol Campbell is used to dividing opinion among Londoners. Many of our city’s football fans worship the former Arsenal star for helping to deliver several Premier League titles and FA Cups to Highbury – and yet thousands of others still resent him for walking out on Tottenham Hotspur to join their fierce local rivals.

A strong-willed and opinionated character, Campbell has decided to weigh in on the referendum debate, calling on Britain to leave the EU. Unfortunately for the ex-England international, his argument contains significantly more holes than the defences he used to marshall.

Campbell, writing in the Mail on Sunday, begins by hailing the extraordinary global success of the Premier League. “This great league has built its success on its unrivalled ability to attract the best of the best from around the world,” he says – before, bizarrely, arguing that it would be even more successful if it reversed this trend by imposing greater restrictions on foreign imports.

The argument is a common one, both in football circles and when it comes to the broader economy. Roughly, it goes as follows – foreign labour, or foreign goods, are all very well when they are of an exceptionally high quality, but the authorities must step in to block “mediocre” imports.

The theory relies on the assumption that governing bodies are capable of deciding which imports will significantly benefit British industry, and which will not. The Premier League offers a neat example of the problems behind such an assumption.

Had Campbell’s proposal been in place, players such as Leicester’s midfield phenomenon N’Golo Kante, or West Ham’s set-piece maestro Dimitri Payet, could have been prevented from coming to the UK – while big-name internationals such as Radamel Falcao and Mario Balotelli, who both flopped specularly in recent seasons, would still have been welcomed with open arms.

Football aside, the Leave campaign needs to be wary of trumpeting protectionist causes. Former business group leader John Longworth suggested last week that the EU was stopping Britain from imposing higher barriers and tariffs on imported steel in order to prop up the ailing domestic industry.

Such soundbites will go down well in many corners of the country, but they contradict the idea that Britain could be a more globally focused, free trade state if only it escaped the socialist fetters of Brussels. Are we leaving the EU in order to tear down trade barriers, or to regain the right to build them?